1. Field of the Invention
This invention relates to improvements in a tack-in selvage forming apparatus for a loom, and more particularly to a device for controllably driving a tack-in needle by which the end portion of a picked weft yarn is tacked in and woven in a fabric.
2. Description of the Prior Art
A variety of tack-in selvage forming apparatus have been proposed and arranged fundamentally as follows: A tack-in needle is attached to a needle shaft which is connected through a power transmission mechanism with a drive cam. The tack-in needle makes its forward and rearward movement in the direction of extension of warp yarns at predetermined timings and makes its reciprocal rotational movement around the axis of the needle shaft at predetermined timings under rotation of the drive cam, thereby catching the weft yarn end portion extending between a selvage structure and a weft yarn end portion retaining device and turning it up into a warp yarn shed opening.
In order to carry out a tack-in operation in weaving a pile structure of towel or the like, the advancing position of a reed is different between a fast beating-up operation and a blind beating-up operation, and therefore the tack-in selvage forming apparatus is required to be moved to accomplish a tack-in operation in each weaving cycle. This makes a high-speed operation of the loom difficult. In view of this, in practice, the tack-in selvage forming apparatus is arranged to be not moved, in which the tack-in needle is driven to take the weft yarn end portions at one time in a plurality of weaving cycles, thereby to tack in a plurality of the weft yarn end portion, at one time. Thus, the tack-in needle is arranged to rest in operation. Such an arrangement is disclosed, for example, in U.S. Pat. No. 4,600,039 entitled "Process and Device for the Formation of a Tucked Selvage, Especially Suitable for Terry Looms".
In the above-discussed arrangement, the needle shaft provided with the tack-in needle is driven through a cam follower which is biased on the drive cam by a spring. Additionally, the cam follower is withdrawn from the drive cam to rest the tack-in needle under the action of another cam. Thus, two different cams are required for driving and resting the tack-in needle. Additionally, since the spring is used to bias the cam follower onto the drive cam, it is impossible to operate the loom at a high speed.